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Grand Teton National Park Report

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Outside its native range, the invasive species Potamopyrgus antipodarum (New Zealand Mud snail; NZMS) has seldom been reported to harbor parasites. To test this intriguing observation, 7 sites along the Snake River and Polecat Creek in the Grand Teton National Park/John D Rockefeller Memorial Parkway area (W yoming, USA) were surveyed for NZMS, native aquatic snails and parasites: digenean trematodes (specialist parasites of snails) and nematomorphs (horse hair worms, generalist parasites of aquatic invertebrates), in July 2005. Non-destructive examination of 96 native snails at each site revealed abundant presence of digeneans (parasites that specialize in snails) at 6 sites. Within 2 hours, up to 12.4% of lymnaeid snails shed furcocercous cercaria or xiphidiocercaria, and up to 50% of physid snails released furcocercous cercaria or echinostome cercaria. A total of ~900 NZMS (collected from 5 of the sites) were investigated for infection with digeneans by overnight shedding. One NZMS yielded amphistome­like metacercariae that had encysted in the observation tray. The dissection of 150 ethanol-fixed NZMS (30/site) revealed several types of internal metacercarial stages of digeneans in 5 snails (all from Polecat Creek). PCR-based assays targeting parasite rDNA sequences in DNA extracted from pools of 150 snails each also indicated associations between digenean parasites and NZMS. All parasites were detected in NZMS from Polecat Creek. NZMS were not observed to harbor nematomorph parasites with any of the techniques used. In conclusion, the sites tested contained multiple native snail-digenean parasite associations, and the capacity of invasive NZMS outside the native range to serve as first and second intermediate host for digenean parasites may have been underestimated previously.